• T. Yellappa

The granulite facies rocks of Southern Granulite Terrain (SGT), India represent lower crust-upper mantle products of different tectonothermal events in different origins. They include charnockites, two pyroxene granulites of mafic-felsic, dismembered ophiolite sequence, mafic-ultramafic intrusions and granitoids. The southern part of the Cauvery Suture Zone (CSZ) around Aniyapuram-Mohanur, near Namakkal is dominated by wide range of mafic-felsic granulites, well exposed in close association with dismembered mafic and ultramafic rocks including peridotite, pyroxenite, amphibolite, gabbro-gabbronoritic rocks metapelite, metachert with younger intrusives of pegmatite and granitoids. The petrology of these granulites are characterized by sub-idioblastic fine to coarse-grained clinopyroxene (40-50%) and orthopyroxene (10-20%), idioblastic garnets (20-30%), subhedral to anhedral amphiboles (10-20%) and plagioclases (5%) with accessory phases of apatite, zircon, biotite and opaque minerals. Whole rock geochemistry of 14 representative samples reveal, the granulites are mafic to slightly intermediate in composition with higher SiO2 (47-53 wt%) and A12O3 (10-16 wt%) with low K2O contents (<0.4wt%). Trace element ratios are extremely variable with very high K/Rb ratios (540-13447) reflected in very low Rb contents (0.2-7 ppm) and varied Ba/La (1.8-43.40), Rb/Sr (0.0001-0.13) and Sr/Nd (3.23-34.25) concentrations. The geochemical variation plots (Na2O+K2O-FeOt-MgO and Zr vs.Y) reveal that these granulites belong to calc-alkaline to tholeiitc signatures. On various tectonic discrimination plots (MnO-TiO2-P2O5, Ti vs.V, Ti vs. Zr, and Cr vs. Y) these show island arc origin. Spider plots with normalized MORB show enrichment of LILE (Sr, K, Rb, Ba) and depletion of HFSE (Ti, Nb, Ta, Hf) with -ve Nb anomalies. The above results with available age data suggest that the protoliths of the mafic granulites are tholeiitic basalts developed in island arc environment related to Neoarchean to Paleoproterozoic suprasubduction zone tectonic setting, consistent with dismembered ophiolite sequence of this region and were subjected to granulite facies metamorphism during Neoproterozoic arc magmatism in the terrain.

Mafic granulites, Island arc, Suprasubduction zone, Cauvery Suture Zone, Southern Granulite Terrain

"Geochemistry of mafic granulites from Aniyapuram Mafic-Ultramafic Complex (Cauvery Suture Zone) Southern India: implications for Suprasubduction zone tectonics", International Journal of Emerging Technologies and Innovative Research (www.jetir.org), ISSN:2349-5162, Vol.5, Issue 8, page no.417-432, August-2018, Available :http://www.jetir.org/papers/JETIR1807307.pdf

"Geochemistry of mafic granulites from Aniyapuram Mafic-Ultramafic Complex (Cauvery Suture Zone) Southern India: implications for Suprasubduction zone tectonics", International Journal of Emerging Technologies and Innovative Research (www.jetir.org | UGC and issn Approved), ISSN:2349-5162, Vol.5, Issue 8, page no. pp417-432, August-2018, Available at : http://www.jetir.org/papers/JETIR1807307.pdf